Method of obtaining sparkless-breaks of electric circuits



T. F. WALL. METHOD OF OBTAINING SPARKLESS-BREAKS 0F ELECTRIC CIRCUITS,

APPLICATION FILED' APR. l9. l lfi- 1,315,886. PiltOllfQdSQPt. J, 1919.

2 SHEETS- SHEET 1.

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. T. F. WALL.- METHOD OF OBTAINING SPARKLESS BREAKS 0F ELECTRIC c;

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APPLICATION men'- APR. 19. 1915.

Patented Sept. 9, 1919.

2 SHEETS-SHEET 2 a e T rains-ea.

Patented Slept. Q lit le.

duplication filed until/l9, it'o. limit 5i.

flb all wit/011i. it may concern." I

Be 1t known that 1. Tribune Fnnonnrcn and lreland, residing at 124- Poplar avenue,

Edgbaston, Birmingham, England, lecturer in electrical engineering at the University of Birmingham, have nvented a certain new and useful Method and Means of Ubtarning Sparkles's Breaks of Electric Gircuits, of

which the following is a specification.

lt 1S well'known that: it a resistanceless inductive circuit be supplied by a symmetrical alternating P. l). and the. circuit'be closed at the instant at which the P. D. passes through its zero value the current in the circuit will attain its maximum value .when the 1?. wave has passed through halt a cycle and thecurrent will sink to zero when the P. D. wave has'passed through one cycle. The result is accordingly that the P. D. and current wave pass simultaneously through their zero values, and consequently it the circuit were .opened at this instant no spark would be produced. Moreover since the current curve is fiat in the neigh borho od of its zero values there .would be little danger of a spark being produced it the brealr did not take place precisely at the til correct instant. The relationship between pressure and current in the cycle under the above mentioned conditions is illustrated at Figure 1, where e denotes the pressure curve c the current curve. As the calculation of the curves is based on the assumption that the circuit is without resistance, thecurrent curve represents a hypothetical case.

In practice it is impossible to obtain inductive coils of which the resistance is Zero and the result is that although the circuit be closed at the instant at which the P. D. is zero the current does not again become zero at the completion of the cycle. Consequently sparkless breaking cannot be ob tained. llhis condition is illustrated at Fig. 2, where as before 'c denotes the pressure curve and i the current curve. It will be observed that toward the end of the cycle the current curve falls below the zero line due to the resistance.

It has been proposed to makeuse of the above known relationship as represented by Fig. 2 in the operation of percussive tools by alternating currents, but it is evident from Fig. 2 that as the pressure and current do not reach the zero value concur- ,rently a sparkless break is impossible. l Vann, sub ect of the King, ofGreat ldritain The object or: thisinvention is to provide a method and a means whereby the above mentioned objectionable efitect of resistance asa secondary battery or a suitable continuous current. generator is connected 1n series with the source" of alternatmg M. F. and with the inductive circuit. llhe result is thatthe inductive circuit IGCBIVGS" a P.- D. which is the resultant of the alternating current pressure and the continuous current pressure. This will clearly give a pressure wave in which the maximum values in one direction will be greater than the maximum values in the opposite direction. By suitably. adjusting the magnitude of the continuous currentcomponent of the pressure applied to the inductive circuit the efiect-of the resistance of the inductive circuit can be compensated so that if the circuit be closed when the pressure is zero the current sinks to zero again at the instant at which the pressure is passing through one of its zero values. This condition is then favorable for opening the circuit. The opening and closing or the circuit at the right instant may. of course, be performed by means of a suitable contact maker.

. calculated example of the relationship ob tained by the addition of a constant P. D. to an alternating P. D. is shown at Fig. 3

- where 6 denotes the pressure and i the current. The alternating component of the P. D. for this example is assumed to be a sine wave. lt will be'noticed that there is habsolute coincidence of the pressure and current Zero values at the end of the cycle, and in consequence sparkless breaking at that instant can be obtained. Owing to the fact that the current curve is flat when it approaches the zero value breaking can be obtained with negligible sparking over a fairly wide time interval before or after the instant of coincidence. Oscillog'raphic tests on actual apparatus prove that, the required coincidence of the zero values is obtained by suitably adjusting the added P. D., and it is found that by properly setting the contact breaker sparking is eliminated.

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this invention is shown at alternator is represented by in 'ti this is secondary battery e .riahle non-inductive resistance for ad- .ing circuit conditions, and the induc-- coil [3. ilr'il insulated disk 6 driven lo alternator shaft in any other conyei' way synchronously with the alternator carries a metal contact segment 7" and pair of brushes lhe length or the sec'inentis such that the brushes may he set to iualre and break the circuit at the correct instants. switch is indicated by it. instead oi cry or a direct current generator there may be used for producing the compensat M. F. a second alternator so com structed and connected to the inductive cir cuit that it injects an 'M. l which will cause the zero value of the current tocoincide with the zero value or the resultant pressure. I

From the foregoing it is evident that for successfully utilizing in practice the pres sure i and currrent phenomena above de scribed after closing an inductive circuit andenabling sparkless breaking to be obtained, it is necessary to produce an asymmetrical pressure wave in order'to obtain the necessary coincidence of the pressure and current zero values.

By an asymmetrical wave 1 mean one in which the maximum value at t ained by the pressure on one side of the zeroline is greater than that attained on the opposite side, or one in which the areas-3 oi the two parts of the wave are unequal.

It is not essential to this invention that l,

is re it Toy that switch may ht intervals means iling the switch.

shown 7 there 13 provided a 1 id switch A a rich also forms arnia ture of a. pair of magnets i and j. The mag;- net is in series with the inductive circuit and is adapted to hold the switch in the closed position. after the circuit has been made until "the circuit is interrupted by the contact f. 'lihe magnet 2' is n series with the circuit of another and smaller generator on which is provided witha synchronously rotated dislr c carrying a segment ,1 acting in conjunction with brushes 9. Both generators are rotated synchronously. A hatter or portion or the battery F) or any other source of suitable M. F. and a resistance c are arranged in, series with the generator e. In order that the: circuit through i may be excited both shortlybe fore and shortly after the main circuit is made the segment f may be slightly longer than the segment p. For some purposes it may he. suliiciently satisfactory to excite the magnet 9'. from the circuit of the generator a and thus dispense with the generator at and segment and brushes associated therewith. By employing the magnets i and j the hand switch can only be closed and opened when no currentis passing through the main circuit. Any other convenient control for the switch may be provided.

The invention is not limited to the arrangements or devices'herein described, as these may he varied to meet different requirements. Further, the invention is not limited to the uses mentioned.

Having thus described my invention what ll claim. as new and desire to secure by Letters Patent is vThe method of insuring a sparlrless break in a circuit comprising; an inductance and a source of alternating electromotive force in series therewith which comprises closing; the circuit when the alternating electrometive force is substantially zerc impressing auxiliary unidirectional e cctrompotive force thereon or such value to cause the current to through zero at substantially the some time as the impressed elcctroinotive force and interrupting the cir 1i"; at the time when both current and electromotive force rou zero.

y whereof ve signed uiy 

